This invention relates to a storage system for obtaining a snapshot of a volume image in a computer system which uses a storage, and more particularly to obtaining of an image of an optional generation volume.
In an information-oriented society, one of the important roles of the storage system that stores information is data protection. A most common method of data protection is so-called backup which stores data of the storage in a backup medium such as a tape library. In the backup, even if data of the operated storage system is lost due to a failure, interference, an operation mistake, or the like, the data of the stored time can be recovered by restoring backup data, whereby damage can be limited to a minimum.
However, a larger capacity of the storage is accompanied by an increase in time necessary for backup. Additionally, in use of high data updating frequency, a difference from the backup data is shortly increased even when the data is backed up once. Thus, backup data must be frequently generated in case that damage will increase. To deal with a file loss caused by an operation mistake or the like, or to prepare for comparison of file contents with a past state, there is a wish to easily refer to data which is periodically backed up.
A snapshot has been a focus of attention as a function to meet such use. The snapshot stores an image of data of the storage operated at the time. The snapshot image can be accessed as a volume different from that of the operated storage.
As the snapshot function, there has been presented a generation management method of a snapshot image in which a data holding unit 1 executes normal reading, a data holding unit 2 stores a snapshot image of the data holding unit 1 at a given time, a data holding unit 3 stores history information containing update data which accompanies data rewriting in the data holding unit 1 after the time of storing the snapshot image in the data holding unit 2, information indicating a generation thereof, and information indicating an update area thereof, and a data reading source selection unit refers to each history information stored in the data holding unit 3 to obtain a store location of a snapshot image to be read according to designation of a generation and an area of the snapshot image to be read, and switches data reading source to one of the data holding unit 2 and the data holding unit 3 according to the store location (e.g., JP 2002-278819 A).